Study On Mechanical Properties Of Fiber-reinforced Cementitious Grouting Material And Rebar Sleeve Grouting Splice

The connection nodes among prefabricated components play a vital role in the construction performance,overall performance and seismic performance of the prefabricated concrete structures.The connection nodes are often located at the key of the structure's stress concentration and load transfer,and it is also the weakness in fabricated concrete structures.Rebar sleeve grouting connection is currently the most common connection method,and is widely used in beam-column nodes,columncolumn nodes,and shear wall connection nodes.However,domestic research in this area started relatively late and is still in the exploratory stage.Engineering applications and design are always limited.In the connection joint,the reinforced bar is anchored and connected in the grouting sleeve by the restraint of grouting material,therefore,the grouting material plays a decisive role in the anchoring performance.However,the exploitation of the existing grout material is incomplet.Excessive pursuit of high strength results in great brittleness and great dispersion.Even the grout available commercially still fails to meet the strength requirements,and lacks the research of grout material toughness for anchoring performance and seismic performance.Therefore,it is of great significance to study and improve the performance of grouting for the further development of fabricated concrete structures.The specific research content includes three levels,as follows:1.Material level-the basic mechanical properties of fiber reinforced cement-based grout:According to the method of control variables,the fiber fitting test of grouting materials was carried out,and 53 groups of tests were designed,each containing 10 test blocks,to test the expansion rate,1d strength,3d strength and 28 d strength.A total of 530 test blocks were tested.Three fiber types were selected: PP,PVA and BF.Set the volume content of the four fibers: 0.1%,0.3%,0.5% and 0.7%,and the length of the four fibers: 3mm,6mm,9mm and 12 mm.According to the test results,the experimental group with the volume content of PP fiber of 0.9% was added.The results show that the larger the fiber content and the longer the fiber length has the negative effects on the fluidity and the different effects on the mechanical properties.However,it is obvious that the fiber increased the toughness of the grouting material without reducing the strength.The PP fiber with a content of 0.5% and a length of 9mm is selected based on various indexes.PVA fiber with a content of 0.1% and a length of 3mm.Basalt fiber with a content of 0.3% and a length of 6mm is used as the optimal fiber parameter.2.Components level-The mechanical properties of fiber reinforced grouting sleeve joints with different anchorage lengths.The experimental study of the mechanical performance of the reinforced grouting sleeve joint is carried out according to the control variable method,and the full grouting sleeve is selected.Based on the material-level study,the optimal performance grout material with three kind of fibers are selected.Different anchor lengths are used to produce the grouting sleeve anchor joints specimens.The research parameters include:(1)four kind of grout material;(2)five kinds of steel bar anchoring length: 4d,5d,6d,7d,8d.(3)Three loading schemes: unidirectional tensile test,high stress repeated tensile and compression test,and large deformation repeated tensile and compression test.A total of 60 groups,each group contains 3 joint specimens,a total of 180 specimens.In the three loading tests,the no fiber grouting joint is pulled out and damaged at 6d anchorage length,which means the minimum anchoring length is 6d.But the minimum anchoring length of the fiber-filled grouting specimens could be reduced to 5d.Among the parts of cyclic loading,the fiber grout joints show lower residual deformation and stiffness degradation performance under the two extreme anchoring lengths of 4d and 8d.For the same failure of bar pull-out,the ultimate residual bond strength of fiber reinforced grout joints increased by 3.8% to 22.8%.3.Theoretical analysis level-the bonding and anchoring characteristics between fiber-reinforced grouting and steel bars in sleeve grouting connections and their economic efficiency.For further explore and verify the anchoring mechanism of the fiber grout material,12 groups of joint specimens are designed and manufactured according to the control variable method to unidirectional tensile test.The parameters include four kind of grouts and three levels of anchor lengths: 4d,6d,and 8d.The results show that the distribution of the bonding stress of fiber grout is more uniform.The no-fiber grout has a "?" distribution at three anchor lengths.The PP fiber specimens bonding stress has a "saddle" distribution at the 8d anchor length,there is obvious secondary peaks appeared when 6d and 4d anchor length.The PVA and BF fiber specimens showed obvious secondary peaks at the three anchor lengths,and when the load is 120 k N and the anchorage length is 8d,the stress distribution shows an "arch" shape.All the peak stress of the fiber-grout is also effectively reduced.The peak bonding stress of the PP-8d fiber specimen was 79.5% of the peak stress of the JZ-8d specimen,and the peak stress of the PVA-8d and BF-8d specimens are 69% and 92.7% of JZ-8d.In addition,the initial stage of PP fiber grouting is relatively high utilized,the grouting material integrity is better.It was confirmed that the fiber can improve the internal force distribution of the grout,reduce the peak stress,reduce the stress concentration,and improve the bearing capacity.The cost of PP fiber grout only increased by 1.23%,PVA and BF fibers increased by 2.98%,the cost of specific amount of fiber to the grout did not increase much,and the performance-price ratio was high.